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Show 1895.] LORIUS FLAVOPALLIATUS AND PSITTACUS ERITHACUS. 369 slightly grooved antero-posteriorly, especially in the anterior portion of each. But in P. erithacus these cannot be said to be more thau rather flattened. The ventral surface of the prosopium, behind tbe palate, shows, in both species, a median antero-posterior ridge with a wide concavity on either side of it, in the hinder part of which is a deepish fossa, beneath which the palatine passes forwards and external to which is the fossa for the zygoma. The median ridge projects backwards as a process from the postaxial margin of this postpalatal part of the ventral surface of the prosopium, which margin is otherwise slightly concave. The median ridge is less marked in L. flavopalliatus and the surface on either side of it is entire, while iu P. erithacus it presents a bony network of diploe. This surface is much longer relatively in L. flavopalliatus. T H E ANTERIOR ASPECT of the prosopium (see fig. 8, p. 382) is very similar in both species. Its outline approximates to that of an isosceles triangle with the base dorsad-the basal line being very slightly convex and the two lateral lines being convex towards tbe base and concave (more strongly so in L. flavopalliatus) towards the apex. In addition to the distinctive characters given in the description of the general anterior aspect of the skull, the following points may be mentioned :-The nares in L. flavopalliatus are more medianly approximated and nearer the uppermost margin of the prosopium than in P. erithacus, while the lamella of bone between each nostril and the tomial margin is relatively wider. In the latter the lachrymal process is more marked and projects more outwards. In L. flavopalliatus it hardly projects at all outwTards, but only backwards. The most considerable difference is the greater extension ventrad of the apex of the prosopium (relatively as well as absolutely) in P. erithacus. T H E POSTERIOR ASPECT of the prosopium (which cannot of course be well seen till this part is detached from the cranium) shows, in P. erithacus, an irregular surface which rises, at a moderately obtuse angle, from the hinder margin of the postpalatal ventral surface of the prosopium. The median ridge just described as existing on that surface is continued upwards (mr) in the middle of the posterior surface with a marked concavity on either side of the vertical grooves, which define, laterally, that ascending median ridge. Externally to this median portion of bone (with its ascending ridge and two lateral concavities) is on either side a large aperture, the two forming the posterior prosopial nares (pn). Each is an oval aperture, longer than broad and inclining outwards towards its ventral boundary. These nares and the whole prosopium are bounded dorsally by a transverse bar of bone (grooved posteriorly), the outer end of which projects outwards and slightly upwards, forming the lachrymal process (Ip). The outer boundary of the posterior nasal opening is formed by a vertical bar of bone (one of the two external nasal crura) which descends from the lachrymal process and outer end of the dorsal horizontal bony bar, first narrowing downwards and then expanding beneath its lower end in the pit for the zygoma. PROC. ZOOL. Soc-1895, No. XXIV. 24 |
